Apparatus, in the form of a eutectic alloy plug (1) and a deployment heater (10) are provided. The plug (1) and the deployment heated (10) are provided with means (5, 13) for releasably retaining the deployment heater (10) within a cavity (4) in the plug (1). The nature of the retaining means is such that once the plug (1) is secured in a well the heater (10) can be recovered without the plug (1). An extraction heater (20), which is also receivable within the cavity (4) of the plug (1), is provided to re-melt the eutectic alloy and thus enable the extraction of the plug from a well. Various method of plugging abandoned wells are made possible by the control that the provided apparatus gives.